Add gmd:protocol, location keywords, & viewer URLs

This update does three things:

1) Adds gmd:protocol elements to all service end points (srv:SV_ServiceIdentification) identifying them as either OPeNDAP:OPeNDAP, UNIDATA:NCSS, OGC:WMS, OGC:WCS, or OGC:SOS--the appropriate valids from this list: https://github.com/OSGeo/Cat-Interop/blob/master/LinkPropertyLookupTable2.csv.

2) Add GCMD Location Keywords from THREDDS catalog metadata: all "geospatialCoverage > name" entries.

3) Adds each "viewer" entry from the THREDDS catalog metadata as an additional gmd:distributorTransferOptions.

John Maurer <jmaurer@hawaii.edu>
Merge pull request #1 from pacioos/patch-1

Add gmd:protocol, location keywords, & viewer URLs